Oral lesions are among the common early HIV-associated opportunistic infections and an important indicator of progression to AIDS. Prevalent among these lesions is oral candidiasis, caused by the dimorphic yeast Candida albicans. The long-range objective of this proposal is to understand the molecular and cellular basis of pathogenesis in oral candidiasis as manifest in individuals with HIV-disease. The immediate objective of this research will be to investigate the correlation between pathogenicity of Candida albicans and its morphological transition between asymptomatic blastoconidial forms in immunocompetent individuals and the development of hyphal forms associated with increased adherence, epithelial invasion and pathology in immunocompromised hosts. These studies will focus on the identification and characterization of molecular probes which can be specifically correlated with either blastoconidial or hyphal forms of Candida: 1. Genes whose products mediate adhesion between Candida cells and epithelial cells or extracellular matrix will be cloned, in particular those which possess characteristics of the beta1 integrin gene family. These will be characterized by DNA sequence analysis, hybrid-arrest translation and immune selection. We will determine the genomic organization of the beta1 integrins with respect to copy number, transcriptional regulation and the presence of potential cis and trans acting regulatory elements; genetic studies will establish their role in Candida adhesion using both in vitro and in vivo assays. 2. cDNA libraries will be developed from blastoconidial, germ tube and hyphal forms of Candida for the isolation of stage-specific mRNA encoding sequences and characterized with respect to sequence, genomic organization and stage- specificity of expression as described above for the beta1 integrin. The hsp70 gene family will be analyzed; these genes appear to be expressed in a stage-specific manner, regulated by growth conditions and stimuli of hyphal development. These transcripts will be characterized with the objective of identifying specific regulatory sequences which, when coupled to appropriate reporters, can be used to monitor the response of stage- and stimulus-specific responses. 3. In collaboration with SCC/OAC the surveillance and characterization of strains in both clinical and epidemiological contexts will be continued, using first the DNA fingerprinting probe CA3, but later incorporating other significant molecular probes generated through this program. These approaches should lead to an understanding of the regulatory complexity of the blastoconidial-hyphal transition and its relationship to pathogenicity, and to the development of molecular reagents useful in identifying those extrinsic and intrinsic factors which trigger the conversion between commensal and symptomatic infections and opportunism.